There is a common need in electrical and electronic devices to provide a voltage step-down between a power source and a load. This is particularly true for devices that receive power from a standard power source, such as mains electricity or a standard battery, but have a lower operating voltage compared to that of the power source.
While there are various different means for providing a voltage step-down, Switching-mode power supply (SMPS) circuits are generally seen as the technology of choice. SMPSs can regulate output voltage and/or current by switching electrical storage elements, such as inductors and/or capacitors, into and out of different electrical configurations at an output stage of the SMPS. It is also common to incorporate transformers into SMPS output stages so that the voltage step-down is in-part performed by the SMPS and in-part performed by the transformer. Such arrangements are advantageous because the SMPS provides tightly-regulated control of the output voltage and the transformer provides electrical isolation between the input and the output. The combined use of the SMPS and transformer also allows for a relatively small transformer to be used.
It is common in various high-power systems to provide a main power source, which is arranged for delivering high powers to a load, and a secondary extra-low voltage (ELV) source, which is arranged for delivering a safe voltage, generally no more than 24V to a load. However, such known systems suffer from various problems. For example, the systems are often large and complex because two different types of power source need to be utilized. High voltage mains power and 24V ELV for backup power. In addition, when such systems switch between power sources it is common for there to be a brief loss of system output power, which is extremely undesirable.